This invention relates generally to injection molding and more particularly to an electrical heater with a melt bore extending therethrough to be mounted between a melt distribution manifold and a nozzle.
As seen in U.S. Pat. No. 5,007,821 to Schmidt which issued Apr. 16, 1991, it is known in hot runner technology to attach a separate plate heater to the rear face of a melt distribution manifold. It is also known to mount a separate electrical heater around a nozzle. While this is satisfactory for some applications, it has the disadvantage that the heat transfer is not very efficient. In cases where more heat is required, it is well known to provide heating elements extending integrally in melt distribution manifolds and in nozzles. While this heat transfer is much more efficient, this has the disadvantage of being more costly to produce.
The applicant""s U.S. Pat. No. 4,433,969 which issued Feb. 28, 1984 shows that it is also known to mount a bushing through which the melt flows between the front face of the melt distribution manifold and the rear end of the nozzle.
Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing a separate removable heater having a melt bore extending therethrough which can be mounted between the melt distribution manifold and each nozzle. This is used to provide less heat in some cases and more supplementary heat in other cases.
To this end, in one of its aspects, the invention provides an injection molding heater having a plate-like body and means to heat the body. The plate-like body is made of a thermally conductive material and has one or more melt bores extending therethrough from its rear face to its front face.
In another of its aspects, the invention provides a hot runner injection molding apparatus having a melt distribution manifold and a plurality of nozzles seated in a mold with a melt passage branching in the melt distribution manifold from a common inlet and extending through each of the nozzles towards one or more cavities. A heater is removably mounted between the melt distribution manifold and one or more of the nozzles. Each heater has a plate-like body and means to heat the body. The body is made of a thermally conductive material and has one or more melt bores extending therethrough from its rear face to its front face. The rear face abuts against the melt distribution manifold, the front face abuts against one of the nozzles, and the melt bore extending through the heater forms a portion of the melt passage.
In a further aspect, the invention provides a hot runner injection molding apparatus having a melt distribution manifold and a plurality of nozzles seated in a mold with a melt passage branching in the melt distribution manifold from a common inlet and extending through each of the nozzles towards one or more cavities. A number of heaters are each removably mounted between the melt distribution manifold and one or more of the nozzles. Each heater has a plate-like body and means to heat the body. The plate-like body is made of a thermally conductive material and has one or more melt bores extending therethrough from its rear face to its front face. The rear face abuts against the melt distribution manifold and the front face abuts against one of the nozzles. The melt bore extending through the heater forms a portion of the melt passage and there are means to separately adjust the temperature of one or more of the heaters.
Further objects and advantages of the invention will appear from the following description taken together with the accompanying drawings.